1. Field of Invention
The present invention relates to a lighting system and a projector. Particularly, the invention relates to a structure of a lighting system having a high efficiency for light utilization.
2. Description of Related Art
A related art projector combines imaging light with a light modulation unit, such as a liquid crystal light valve, and projects the combined and enlarged light image on a screen from a projection optical system including a projection lens. In a lighting optical system used in such a projector, light emerging from a light source, such as a metal halide lamp, is randomly polarized light. However, a liquid crystal projector including a liquid crystal light valve using polarized light utilizes only polarized light in one direction for display. When light from the light source is incident on the liquid crystal light valve, merely a half quantity of light is absorbed in a polarizing plate at the light incident side, the absorbed light being not utilized for display.
In order to enhance the efficiency for light utilization, a related art liquid crystal projector is provided with a polarization conversion device provided between the light source and the liquid crystal light valve to convert randomly polarized light from the light source to unidirectionally polarized light that is used for display. A polarization conversion device that is generally used is a polarized beam splitter (PBS) array. The PBS array is a combination of a plurality of PBSs, each having a polarization beam separation film and a reflective film, and a retardation film such as a ½ wavelength film. The PBS array has a function that one of the p-polarized light component and the s-polarized light component contained in the light from the light source is converted to the other.